Running headlights off battery how big of battery?

[TylerL]

I've got a motorized bike like Pablo's and I bought two headlights that draw 55 watts a piece, that's about 9 amps total. My bike has a rack that supports 55lbs, so it can hold a rather large battery if needed. I'm looking to run both lights for about an hour on one 12v battery.

I think I need a 10 amp hour battery, but does it work like that? It seems too easy.

 

[oilyriser]

You might need a 12 Ah battery, since fast drains give lower capacity. LED headlights would be neat, and not need such a heavy battery.

 

[wcbcruzer]

A 10 amp-hour battery would supply 10 amps for 1 hour. So yes, that's all you'll need. Do they sell deep cycle batteries for your bike? If so, that's what I'd get since they are designed to tolerate extreme drains and still be charged as opposed to a regular battery that would no longer be good if you drained it. However, I'd still opt for something more than 10 amp-hours since you never want to actually drain your battery and the more times you run it low, the shorter the life of the battery.

 

[Colt45ws]

Yeah, I'd go with something reasonably bigger. 12 to 14Ah. Just for the extra buffer. Try to avoid running the battery below 12VDC, as this can lead to an untimely death to the battery.
http://jgdarden.com/batteryfaq/carfaq1.htm
Mostly its talking about car batteries, but It has some general tips.

 

[moribundman]

Originally Posted By: TylerL
I've got a motorized bike like Pablo's and I bought two headlights that draw 55 watts a piece, that's about 9 amps total. My bike has a rack that supports 55lbs, so it can hold a rather large battery if needed. I'm looking to run both lights for about an hour on one 12v battery.

I think I need a 10 amp hour battery, but does it work like that? It seems too easy.


Why would you need two headlights with 55 W on a bike? A 10 W halogen light (MR 11 bulb) or 20 W (MR16 bulb) is plenty for up to 25 mph.

build your own light

 

[Colt45ws]

Now that you brought it up. That does seem like alot for a bike. I think even one of those 55W lights would be more than enough.. You might also add a LED taillight or similar.

 

[eljefino]

One 55 watter is enough for me. Cars really stay away, maybe b/c the bulb isn't shielded it's kind of like a high beam. Might be cool to run a 5 watter or white LED "low beam" just in case your bulb blows or to have something to save battery power in the city.

If you run a "happy time" you can run a $3 12v marker light for a tail off the magneto white wire. Advance auto/Parts america has a beehive style that looks like it belongs in a 59 caddilac tailfin.

Incidentally my 7.5 ah gel cell would last ~1.5 hr with my 55 watt foglight, but my night commute is only 45 minutes which is perfect for not going "too deep" in the battery.

 

[TylerL]

LED lights would be nice, but bright LEDs are costly. I'm just a poor college kid.

I bought a pair of lights so I may use both, but if I only need one then I'll just half the battery suggestion.

One 35 watt H3 bulb would most likely be enough light, but those cost over $10 a bulb.

The difference between gell cell and AGM batteries

That taillight is cool, I might have to get one of those.

Thanks guys for all your help.

 

[meep]

NEVER TAKE A LEAD-ACID BATTERY TO FULL DISCHARGE. It destroys them. Typical starter-duty batteries only use 20% of their charge maximium (down to 80%). mixed-duty starter/deep cycle no more than 50%. Dedicated deep cycle no less than 20%.

Sounds like you need a deep cycle, 20AH. Might try wheelchair batteries. Would definenly suggest AGM due to safety. You can find these used for $20 at some battery centers.

M

 

[TylerL]

Bought a used 12Ah battery for $25 shipped. I try not to take it below 12volts. Only running one 55watt light for now, will add a taillight to the back of the rack soon.